This application relates to wireless communication systems and techniques based on code division multiple access (CDMA), and in particular, to system architecture and configurations, management, controls, and operations of trunking systems for CDMA wireless communication.
Wireless communication systems use electromagnetic waves to provide communication with and between mobile communication devices, such as mobile phones. In CDMA systems, a spread spectrum technique is used to allow multiple mobile wireless devices to simultaneously occupy the same frequency spectral range without interference with one another. The bandwidth of this common transmission spectral range is intentionally made much wider than the minimum required signal bandwidth in a communication system. The power of each subscribed mobile wireless device is spread over the wide bandwidth. The spreading results in a relatively low power spectral density and thus reduces the adverse interference to another narrow band signal occupying the same frequency range.
Direct sequence CDMA systems use different code sequences in the forward and reverse links for spectrum spreading. In the reverse link from a mobile device to the network, a transmission signal from each subscribed mobile wireless device in a CDMA system is modulated with a unique pseudo-noise (PN) binary sequence code, which is essentially orthogonal to any other PN sequence designated in the system. This modulation causes the spreading over a wide bandwidth. The orthogonality of different PN sequence codes allows for multiple access within the same frequency spectrum and makes CDMA systems less vulnerable to interference. One unique feature of CDMA systems is that no definite limit exists on the number of users in the system. In practice, the PN sequence codes may not be perfectly orthogonal and the noise caused by cross-correlation of the PN sequence codes can set an upper limit on the system capacity. In the forward link, a transmission signal from each base station to a subscribed mobile wireless device is modulated with a unique Walsh code and is further scrambled with a PN code.
Similar to other communication systems, CDMA systems can use trunking techniques to have a number of users to share a relatively small number of communication paths. This sharing of system resources can improve the system capacity and increase the efficiency in utilizing the system resource. However, the degree of sharing in a trunking system tends to be restricted, in at least one aspect, by the desired grade of service measured by the ability of a user to access a trunked CDMA system, especially during a high traffic period. Moreover, maintaining the privacy of each user's communication may also present a constraint on the degree of sharing in a CDMA trunking system. Hence, proper trunking system design and implementation are important in CDMA systems and are becoming even more so as CDMA systems are migrating from primarily narrowband digital voice communication services to addition of broadband packet data services.